1. Field of the Invention
The present invention relates to a lithographic mask capable of providing regions of graded exposure, such that when combined with anisotropic etching provides three dimensional microstructures of arbitrary size and shape (generally non-prismatic). The present invention also relates to a method for producing a gray-scale x-ray mask and fabricating a tool useful in the preparation of plated molds, or embossing stamps, for printing fine structures into plastic substrates.
2. Description of Related Art
A variety of methods are presently known for making microparts. In particular, U.S. Pat. No. 5,501,893 to Laermer, et al., describe a lithographic technique for etching silicon, generally referred to as “anisotropic etching,” where it is possible to achieve deeply-extending trenches while simultaneously providing side walls which are as nearly parallel and vertical as desired. In particular, Laermer, et al., ('893) teach a multi-step, two stage process for alternately etching an exposed silicon surface in a reactive ion plasma followed by coating the etched surfaces with a thin polymerized layer, wherein the polymer coating serves to protect the wall surfaces of the trench from action of the plasma.
Commonly owned U.S. patent application Ser. No. 09/636,002, filed Aug. 9, 2000 now U.S. Pat. No. 6,477,225 and herein incorporated by reference, discloses a method for preparing an x-ray mask prepared by utilizing an anisotropic deep etching technique. The x-ray mask of the '002 application discloses an x-ray absorbing structure incorporated into the bulk thickness of a standard silicon wafer to provide a robust processing mask capable of withstanding repeated handling.
Finally, U.S. Pat. No. 6,075,650 discloses to prepare a photoresist with a spatially variable dose of electromagnetic radiation to create a surface-relief structures upon developing the exposed resist. The '650 patent also discloses a gray scale mask exposure method, and methods incorporating moving apertures. Not disclosed, however, is a description or suggestion for creating a metal stamping tool by utilizing an etched substrate as a plating base.